This invention relates to a method of manufacturing metal diboride ceramics.
Metal diborides, particularly TiB.sub.2, ZrB.sub.2 and HfB.sub.2, are used for a wide range of applications because of certain properties that they have. For example, they have a high degree of resistance to corrosion by a molten metal and are, therefore, used for making a container for holding a molten metal, or sensor members which are brought into contact with a molten metal. They are also an electrical conductor and are, therefore, used for making electrodes for a molten metal.
The majority of these metal diborides, however, have a melting point which is as high as about 3000.degree. C., and are difficult to sinter. In order to make a sintered product of high density, Japanese Patent Publication No. 43966/1979 proposes a sintering method employing a pressure which is as high as 1000 atm., and Japanese Patent Publication No. 3997/1983 proposes the addition of a substance having a low melting point. However, the method employing such a high pressure is difficult to adopt for making a large product, since an appropriately large apparatus is still difficult to construct and operate safely. The addition of a different substance having a low melting point results in the formation of a sintered product which differs in composition from what is intended, and which no longer retains the excellent properties of a metal diboride. It makes it difficult to obtain a sintered product which is satisfactory in both mechanical properties and electrical conductivity. Moreover, the low-melting substance which retains its original form in a sintered product lowers its resistance to corrosion by a molten metal, as its corrosion is likely to start where the molten metal contacts any such substance.